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    Toxic Algae vs. Harmless Algae

    There are many types of algae that can appear in different forms and colors. The only way to know for certain if an algae bloom is toxic is through testing, but there are some clues to look for. Filamentous algae are generally harmless, while certain types of planktonic algae may produce toxins.

    Home testing options include the stick test, jar test, or a blue green algae test kit. If no toxins are detected, treatment with a copper based algaecide is recommended. If toxins are present, a copper algaecide such as Mizzen is still effective, but treatment should be applied to small sections at a time to prevent releasing too many toxins at once.

    For case-specific guidance, please contact us at 763-428-9777 (option 2).

    Types of Algae

    Filamentous algae generally do not contain toxins. These types of algae start growing on the bottom of the pond or lake, then bubble up to the surface and often settle as mats. They can look stringy, like hair, or wet wool floating. Filamentous algae are typically dark or bright green to yellowish green.

    Some forms of planktonic algae can contain toxins. Planktonic algae do not form strings or filaments, they float freely throughout the water column. These algae can make the water look like pea soup or like paint or oil has been spilled in the water.

    Planktonic algae can be varying colors from red to brown to blue to green. Most often, the blue green algae are those that may contain toxins. If you see blue green algae, at home tests can be done to get another clue whether the algae may be dangerous or not.

    Algae Tests

    Stick Test

    First, find a sturdy stick that’s long enough to put into the water without getting algae on your hands. Hold one end of the stick and put the other end into the water under the algae mat. Slowly pull up the stick.

    If a pile of green stringy algae is stuck to the stick, it is filamentous algae and is most likely completely safe, although it can be a nuisance. If the stick looks like it has been dipped in paint, it is likely blue green algae. While most blue green algae are safe, another test can be done to offer another clue.

    Jar Test

    To conduct this test, get waterproof gloves and a clear jar with lid, pint or quart sized are perfect. Wearing the gloves, dip the jar into the water just below the surface. Avoid getting a sample of only what’s on the surface, be sure to get a few inches in the water. Fill the jar about three-fourths full. Do not fill completely, as algae give off gases that need room in the jar. Wipe off the outside of the container, screw the lid on, and refrigerate it overnight undisturbed.

    The following day, carefully remove the jar to see where the algae have collected. If most of the algae are settled at the bottom, it is likely that there is not a large population of blue green algae in your water body. However, if a green ring has formed at the surface, a blue green algae bloom may be in progress in your water.

    Just because there is an algae bloom does not indicate the presence of toxins. The size of the bloom in addition to the presence of toxins factor into whether the algae can be harmful or not.

    Blue Green Test Kit

    A more scientific way to test algae for toxins is a blue green algae test kit. It tests for hepatotoxins and is 99% accurate. Each kit is one time use and comes with everything needed. Directions are on the package. Fill the test tube, wait for the chemical reaction (10 minutes), drop one drop onto the provided cassette, and then look at the results.

    If the results show toxins are present, keep people and pets out of the water. Treat the algae bloom in small sections until algae are gone and another test kit shows no toxins present.

    Treatment

    If the algae bloom in question is filamentous algae or does not contain toxins, treating with a chelated copper algaecide such as Mizzen is recommended. Treat one-third to one half of the water body at a time two weeks apart to avoid oxygen depletion for fish. If trout, koi, or channel catfish are present, an alternative such as Cape Furl is recommended.

    Treating a toxic algae bloom is complex. As algae die, any toxins present are released, and some of those toxins may be harmful to humans or wildlife. Your local university’s extension office may be able to offer further testing or other personalized guidance.

    Treating small sections of the bloom at a time is best. Copper algaecides give the best control, with copper complexes like Mizzen giving even better control than copper sulfate. Mizzen will help control nearly all types of planktonic and filamentous algae as well as complex branched algae like Chara.

    Summary

    Filamentous algae start growing on the bottom and form stringy mats that can float on the top of the water. Planktonic algae have no structure and can look like spilled oil or paint. Toxins can be present in planktonic algae, not filamentous. The only sure way to know if toxins are present is to get the water tested. Treatment is similar: if there are no toxins, use a copper algaecide, treating no more than one-third of the surface at a time. If there are toxins, consult a local agency for personalized help, and treat small sections of the bloom at a time.